This study is concerned with the effects of chronic obstruction on the function of kidney tubules. Other investigators have suggested that chronic obstruction activates a tubulo-glomerular feedback mechanism which causes glomerular blood flow to a blocked nephron to decrease. The mechanism is not understood. Experiments will be carried out in anesthetized rats using micropuncture and microdissection techniques. Specifically, I will assess glomerular blood flow to blocked and normal tubules using microspheres and microdissection of single nephrons. The change in blood flow with varying durations of blockage (1 hr to 24 hr or more) will be evaluated. Also, I will estimate glomerular capillary pressure (using the stop-flow pressure method) as a function of blockage duration. The effects of a chronic high salt intake on the feedback response will be studied. The experiments should elucidate the time-course of glomerular capillary blood flow and pressure changes which occur following blockage as well as possible involvement of the renin-angiotensin system in the feedback response. BIBLIOGRAPHIC REFERENCES: Tanner, G. A., and S. Sophasan. Kidney pressures after temporary renal artery occlusion in the rat. Am. J. Physiol. 230: 1173-1181, 1976. Tanner, G. A., and M. Steinhausen. Tubular obstruction in ischemia-induced acute renal failure in the rat. Kidney Int. 6: S-65-S-73, 1976.